A broadcast channel detection system is a system essential for successively searching through a large number of channels and detecting a broadcast channel among them, that is, a so-called “channel search”, or for storing in advance a receivable plurality of channels of broadcast stations for each area and enabling a desired broadcast station to be received later by a simple selection operation, that is, “auto preset”. In particular, for example, in a digital broadcast receiver such as a ground digital broadcast receiver or satellite digital broadcast receiver required to quickly capture only broadcast channels among an extremely large number of predetermined channels such as for example 50 channels, the broadcast channel detection system plays an important role.
As the conventional basic elements making up this broadcast channel detection system, there are
a) a station selecting tuner,
b) a mode/guard search unit, and
c) an OFDM frame synchronization unit.
The a) station selecting tuner is a circuit component for individually receiving the predetermined plurality of channels one by one and is a front end component comprised of a so-called high frequency amplification unit, frequency conversion unit, filter, etc.
The b) mode/guard search unit is a circuit component receiving as input a frame signal received by an OFDM (Orthogonal Frequency Division Multiplexing) receiving system suitable for forming a digital broadcast receiver and (i) searching for the “mode”, that is, whether the frame signal has been received under one of the various types of transmission modes of the mode 1, mode 2, and mode 3, and further (ii) searching for the “guard”, that is, the phase of appearance of a so-called guard interval for preventing interference between a so-called effective symbol and the adjoining effective symbols.
The c) OFDM frame synchronization unit is one of the important circuit components forming the OFDM demodulation unit in the OFDM receiver. If frame synchronization is established for the received signal of a selected channel, it is confirmed that this received signal is a received signal of one of the broadcast waves. After this confirmation, the received signal is converted from a signal in the time domain to a signal in the frequency domain, then is demodulated by OFDM by an OFDM demodulation circuit after FFT (Fast Fourier Transformer). Further, it is decoded by an MPEG (Moving Picture Experts Group) decoder and used to reproduce video/audio information to provide video (TV) information and audio information to the user.
The broadcast channel detection system of the digital broadcast receiver covered by the present invention is utilized for example for the “channel search” etc., so it is crucial that the broadcast channels be found at a high speed. Unless this search can be performed at a high speed, the user will end up feeling dissatisfied.
Note that as known publications related to the present invention, there are for example the following [Patent Document 1] to [Patent Document 4].
[Patent Document 1] uses one tuner to receive one station and simultaneously searches for other stations by another tuner, [Patent Document 2] divides a scanning band into two and uses two tuners for separate auto presetting, [Patent Document 3] compares the audio output of two tuners and prevents doubly automatically storing programs of the same content, and [Patent Document 4] uses two tuners alternately for searching and auto preset.
[Patent Document 1] Japanese Patent Publication (A) No. 2002-320165
[Patent Document 2] Japanese Patent Publication (A) No. 5-218811
[Patent Document 3] Japanese Patent Publication (A) No. 7-231245
[Patent Document 4] Japanese Patent Publication (A) No. 10-150346